1. Field of the Invention
The invention relates to a method for forming a periodic structure, such as photonic crystal, and more particularly relates a method for forming a periodic structure in a light-emitting device.
2. Description of the Related Art
Optoelectronic technology has rapidly developed, and is currently in wide usage, thus improving the wellbeing of mankind.
In recent years, due to structure and process development of photonic crystals, application potential for photonic crystals has increased. Basically, photonic crystal is a structure with a periodic varying refractive index or dielectric constant and simulates arrangement of atoms in a solid crystal. Photonic crystals are similar to the energy gap of electrons in solid crystals and generates energy gap of photons therein. Hence, transmissive characteristics of electromagnetic waves, such as amplitude, phase, polarization or wavelength, can be changed by adjusting characteristics of photonic crystals.
Some research has shown that lighting efficiency of a light-emitting diode can be greatly increased by applying photonic-crystal technology to the light-emitting diode. However, fabrication of photonic crystals must use patterning technologies with very small sizes, wherein the size of a photonic crystal is about ¼ that of a wavelength of a light signal in a material, Note that the size for patterning technologies for most optoelectronic applications is about 25 nm˜100 nm. Photonic crystals are mainly fabricated by an electron-beam lithography (EBL) and dry etching process to form air holes in a III-V semiconductor. The equipment for forming photonic crystals are very expensive and have low production rates, such that photonic crystals are yet to be mass produced and applied.